A main communication method is changed from a wire communication to a wireless (radio) communication. Recently, a portable Internet technology has been actively developed to overcome limits of the related art radio communication. This portable Internet technology indicates a service which enables a user to use high-speed Internet without limitation of time and place. That is, the portable Internet technology is a new kind of communication service, which is created by combining advantages of both mobile phone and wireless LAN.
A portable Internet service using a radio communication channel supports high-speed and high-quality data service based on IEEE 802.16 technology standard. Most of causes of hindering the high-speed and high-quality data service in the radio communication result from wireless channel environment. The wireless channel environment may be frequently changed not only by white noise but also by the signal-power change by fading, the shadowing, the Doppler effect by the frequent movement and speed change of portable terminal, and the interference by other users and multi-path signal.
The change of wireless channel environment affects a transmission quality of wireless communication system. For providing high-speed and high-quality radio data packet service under the environment of communication service using the above wireless channel, there has been proposed a method of correcting the packet transmitted, for example, Hybrid Automatic Repeat Request (hereinafter, referred to as ‘HARQ’) method.
The HARQ method basically tries correcting errors in received codes, and determines whether or not the code is re-transmitted by the use of simple error-detection code such as CRC (Cyclic Redundancy Check).
The transmission quality via the wireless channel may be determined based on the reliability of data received in a receiving unit. The channel reliability may be defined by a packet error rate or frame error rate.
In case of the IEEE 802.16 technology standard, the services may include five kinds of Unsolicited Grant Service (UGS), Real-time Polling Service (rtPS), Extended Real-time Polling Service (ertPS), Non-real-time Polling Service (nrtPS), and Best Effort Service (BE service), on the basis of QoS request in the respective services. Among the above five services, the UGS, ertPS, and rtPS are included in the real-time service; and the nrtPS and BE service are included in the non-real-time service. These services have QoS parameters of minimum transmission rate, maximum latency, jitter, and maximum sustain rate values in traffic.
There are many differences of QoS parameters between the real-time service and the non-real-time service. Among the many differences, especially, the largest difference between the real-time service and the non-real-time service may be referred to as latency. In consideration to latency condition, the traffics of the real-time service have the following properties.
Generally, a real-time traffic has a higher priority than a non-real-time traffic so to satisfy the latency condition.
In case of the real-time service, supposing that the latency condition (latency condition and jitter condition in the UGS and ertPS) is not satisfied in the corresponding packet. In this case, even though the corresponding packet is successively transmitted, the corresponding packet cannot be used. For satisfying these conditions, there is a need for a carefully designed scheduling algorithm for the real-time service.
From the viewpoint of loss packet error rate, the real-time service is less sensitive than the non-real-time service. However, when the HARQ mechanism is designed and implemented, not much consideration is given for this less restrictive requirement for latency in case real-time service is provided. That is, the re-transmission for all erroneous packets is requested even under the favorable condition when the permitted packet error rate (PER) for the real-time service is being satisfied. This causes the undesirable extra latency so that the efficiency of communication system is deteriorated.